No idea how busy the road is or db levels, but I don't think a hedge will reduce the noise by any significant margin other than visually screen it of course.
I was taught at college that you would need at least 50m dense planting to significantly reduce traffic noise. Not sure if that's spot on figure and I'm sure someone on LJN will know but I do remember it was a colossal amount of hedging.
Other ways of dealing with traffic noise are to install features which themselves make noise as a more pleasant distraction, such as a water feature or even chimes.
leylandi is a great noise reducer also 12 months of the year ! , to 2nd that a laural would be not as good but ok